Tumour immunology Flashcards
which cells attack tumours?
- CD8+ T cells
- Natural killer cells
how do t cells recognise infected or malignant cells
through major histocompatability complex molecules on antigen presenting cells
what are the three professional antigen presenting cells
- Dendritic cells (majority)
- Activated macrophages
- Activated B cells
give four features of MHC class 1
- Found on almost all nucleated cells (not onrbc or germline cells)
- Present endogenous antigens (intracellular, internal)
- Display self proteins, virus proteins, intracellular pathogens
- Present antigen to cytotoxic T cells (CD8)
give four features of class 2 MHCs
- Found primarily on Antigen presenting cells (APCs)
- Present exogenous antigens (extracellular, external)
- Phagocytosis, receptor mediate endocytosis
- Present antigen to helper T cells (CD4)
give four features of class 2 MHCs
- Found primarily on Antigen presenting cells (APCs)
- Present exogenous antigens (extracellular, external)
- Phagocytosis, receptor mediate endocytosis
- Present antigen to helper T cells (CD4)
what two signals are needed for t cells to be activated?
antigen
costimulation from an apc
what are the surface molecules and secreted molecules of CD4+ helper T cells
TCR, CD3, CD4 = surface molecules
IFNgamma, IL-2, IL-4, IL-5, IL-13, IL-10
what are the surface molecules and secreted molecules of CD8+ killer T cells?
TCR, CD3, CD8 = surface molecules
perforin, granzyme, IFN gamma
what are the functions of CD4 T cells?
- immunity against intracellular bacteria and parasites
- provide help to CD8 T cells
- promote humoral immune responses
what are the functions of CD8 T cells?
- when activated they become cytotoxic
- kill virally infected cells
- kill tumour cells
what combinations of signals allows NK cells to attack?
activating ligand but not MHC = attack
activating ligand + MHC = attack
How do NK cells make the decision to attack?
based on the balance of activating and inhibitory signals
describe the mechanism of perforin
When the NK cell approaches the target cell, secretory granules of perforin (&granzyme) accumulate towards it. Microtubules draw them towards the edge of the cell via secretory granule trafficking
Fusion of granules with the presynaptic membrane allows release of perforin (&granzyme)
Perforin then is able to polymerize and form a channel in the target cell membrane to enter the cell (needs Ca2+)
what needs to happen for a neoantigen to be made?
mutation needs to be generated, translated to protein, a peptide needs to be generated by the proteosome and pass into the ER. the peptide then needs to be bound by an MHC class 1 molecules.
what neoantigens can be recognised by T cells to initiate a response?
- mutated antigens
- overexpressed antigens
- germline antigens
- viral oncoproteins
what percentage of tumours are triggered by viruses?
about 15%
why are patients tissue more variable than using mice or cloned tumour cell lines?
- We use identical mice and only a few very in-bred mouse strains
- We use a few tumour cell lines, that are often extremely mutated after years in culture
- We inject at millions – the tumours grow within weeks rather than years like in real life
-
what is one way of telling if T cells have an important anti-cance roles in patients?
what have the results shown us?
monitoring if patients on immunosuppressive therapies have an increased cancer risk
Some cancers increase in frequency if you are on immunosuppressive drugs
Risk sometimes disappears when they come off the immunosuppressant dugs and their t cells come back up again
transplant recipients on long temr immunosuppression have a greater risk of non-hodkinlymphoma and liver cancer possibly due to increased infection with some viruses
increased risk of lung and kidney cancers was also seen unconnected to infection
what are the four grades used to score immune cell infiltration (TIL) in human cancers
Grade 0 - no TIL
Grade 1- few
Grade 2 - moderate
Grade 3 - marked
how did the TIL grading correspond to survival rates?
grade 3 (with marked TIL) had 100% survival rate, the lower grades with fewer TIL had a worsening level or survival with the worst being Grade 0 with no TIL
how is the immunoscore determined?
take biopsy of tumour
section it and scan to look for T cells
the immune cells infiltrating the tumor are counted - those in the center of the tumour and at the invasive margin
both are important for outcome - no1 predicter of survival is whether you have T cells in the centre
what type of T cells give you a 5x chance of survival if they are present in the centre of your tumour
granzyme t cells
what t cells have a poor effect on prognosis?
Th2
Th17
Treg
what t cells have a good effect on prognosis?
CD8+
Th1
what is the main role and condition caused by Th1 cells
intracellular pathogens
chronic inflammation
what is the main role and condition caused by Th2 cells
extracellular parasites
allergic disorders
what is the main role and condition caused by Th17 cells
extracelluar pathogens
autoimmunity
what is the main role and condition caused by Th22
wound healing
inflammatory diseases
what is the main role of T reg cells
self tolerance
give examples of hot tumour types
melanoma, kidney, bladder, head and neck, non-small cell lung cancer
give examples of cold tumour types
most breast cancers, prostate, pancreatic, glioblastoma, ovarian
Hot tumours have a __ mutational burden
hot tumours have a high mutational burden
what are the two kinds of cold tumours
those where immune cells are excluded
and those where the tumour is ignored and there are no immune cells
what three things makes a tumour antigen
- not normalling expressed or highly expressed
- a peptide that bind to MHC1 or MHC2
- AND induces T cell activation
what are the three broad groups of tumour antigens
- tumour associated antigens
- tumour specific antigens
- unconventional antigens
give three types of tumour associated antigens
- germline antigens: on germline and placenta cells which do not express MHC but only SEEN in tumours (expression fue to altered DNA methylation)
- HERVs: make up 8% of genomic DNA but are normalling epigenetically silenced. expressed due to DNA methylation alterations.
- overexpressed antigens: products of normal genes expressed in other tissues and overexpressed in cancer
describe HERVs and the pros and cons of therapeutically targetting them
a family of viruses (DNA) that make up 8% of our genomic DNA but are normally epigentically silenced
expressed in tumours due to DNA methylation alterations
they are immunogenic so some of the peptides will be recognised
virtually all cancers express these peptides but limited clinical experience in targetting them - they can be expressed inother tissue so very careful screening is necessary (off target toxicity possible)
in terms of structural similarity to normal tissue proteins and expression among different patients, what would be an ideal antigen to target
those with low structural similarity to normal proteins
and is shared among patients
what is the major downside of therapeutically targeting overexpressed antigens
high risk of on-target tocicity
targets the right tissue but causes a lot of problems
give four types of tumour specific antigens
- single nucleotide variables
- INDELS (insertions and deletions)
- gene fusions (some are pan cancer)
- viral oncoproteins
give some pros and cons of therapeuticallu targetting tumour specific antigens
pros- least chance of off target toxicity
viral oncoproteins recognised by T cells
immunogenic
some gene fusions are pan cancer
high proportion of INDELS generate high affinity MHC binding peptides
cons - only 1.5% of mutated single nucleotide variables are immunogenic and 99% were unique to each patient (difficult to manage in clinic
specificity/unique to each patient so more expensive
give three unconventional antigens
- splice variants: aberrant mRNA splicing can result in intron retention or novel exon-exon junctions
- cyptic antigens: result form tranlation of coding gens in alternative ORFs or fom translation of non-coding sequences (mostly due to leaking scanning)
- post- translational changes: peptides could also go through phosphorylation / acetylation / citrullination / glycosylation / deamidation. or fusion peptides from proteosomal splicing of two peptide fragments
what are the three models for cancer stem cells
they are like normal stem cells, fixed and developmentally hierarchical
stochastic: random and variable
dominant subclone: dynamic, subclone genetic advantage and selection
what are the three stages of immunoediting?
- Elimination – Tumour cells are targeted by both the innate and adaptive immune system, many tumour cells are destroyed
- Equilibrium – Tumour cells are controlled by the immune system, but not eliminated
- Escape – Tumour cells acquire new mutations that allow them to escape the immune response
describe the experiment that shows that the immune system driven tumour cells to become less immunogenic
mice were given tumours via a carcinogenic drug
these tumours were grown in wild type and Rag-/- mice.
then transplanted into different types of mice
the tumours grown in mice with no t cells (Rag-/-) and put into normal mice don’t grow - because they havent undergone immunoediting, they havent had any T cells to avoid, making it easier for the immune system to kill it
give five ways that tumours are actively immunosuppressive
1 loss of MHC
2 VEGF (suppressive)
3 FasL (kill t cells)
4 suppressive cytokines (TGFbeta, IL10)
5 PDL1 – PD1 (turns off t cells)
how does MHC downregulation hide antigens?
TAP dimer chaperones peptide into the endoplasmic reticulum
Tapesim loads them into the mhc molecule
Calreticulin and calnexin support the development of the MHC molecule
For MHC class one you have the addition of beta2 microglobulin?
Knocking out any of these proteins would prevent mhc being exhibited
to stop the mutated peptide from becoming an antigen or
(fewer MHCs to present the antigens to the T cells)
T cells cant see the tumour cells without mhcs
NK cells can still see it however there are fewer of them and there are less of them
what are the five forms of MHC downregulation?
- total loss
- selective loss
- hapolotype loss
- total downregulation
- selective downregulation
how are TILs prevented from migrating into the tumour?
CXCR3 signalling is important for T cells binding to endothelial cells and moving into the tumour
Tumours disrupt this chemokine production to prevent TIL migration or to attract suppressive cells like macrophages
Stop production or subvert it, producing chemokines that brings in macrophages CSF1 and CSF2 (name changed) (protumour)
how do tumours kill the T cells that make it in to the tumour?
they express the Fas ligand (upregulated compared to normal tissues)
if Fas bind Fas ligand and dimerises it causes apoptosis of the T cell (by activating Caspase 8)
how do tumours dampen the T cell response?
they make growth factors like VEGF and bFGF to block the adhesion molecule expression that T cells use to see it and enter through the endothelium
list the molecules and receptos that can inhibit t cell activation
- PD-L1
- PD-L2
- IDO
- CD31
- Tim3
- PGE2
- IL-6
- IL-10
- VEGF
what receptors/ligands can kill T cells?
2
- FasL
- TRAIL
what is involved in treating a patient with adoptive T cell therapy?
o Adoptive T cell therapy involves removing a patient’s tumour-infiltrating lymphocytes, selecting effective tumour-specific ones (eg high granzyme), expanding them ex vivo and infusing them back in
o Before the infusion patients are treated with lymphodepleting chemotherapy (no. of t cells kept in check)
o Along with the TIL, IL-2 injections are given to support the growth of the T cells
what is the major side effect of adoptive t cell therapy?
severe side effects due to cytokine storm - owing to cytokine release by the T cells
particularly capiliary leak syndrome which can lead to multiple organ failure
what are CAR T cells?
chimeric antigen receptor T cells
T cells transfected (eg using lentivirus) with the variable chain of an antibody specific to a tumour antigen
(particularly good for HER or alternatively glycosylated antigens)
what activating cytokines are thought to be useful to infuse into a tumour?
o For proliferation and survival of all T cells IL-2 is absolutely critical. Taken up through the IL-2R (CD25 and other chains)
o For activation, IL-12 and IL-15 promote Th1 cells and activate NK cells
what is the major side effect of infusing activating cytokines?
cytokine storm (can cause multiple organ failure)
why hasnt the therapy to increase T cell priming by DC been very successful?
o Adoptive transfer of DC + antigen is much harder than transfer of the T cells – they are fewer in number, must get to the right area of the lymph node to trigger T cell proliferation, must have all the correct co-receptors
o This has been tried for decades but positive results are scarce – it works much better in mice than in humans, for reasons we don’t understand well
what are the four ways the therapy to increase in T cell priming has been attempted?
o Enhance TAA presentation
o Enhance lymph node migration (miR-500, CCR7)
o Combat immunosuppression (CD40l-> IL-12, IFNgamma))
o Enhance tumour recruitment (CCL21, CXCL19, XCR1)
what is oncolytic virus therapy?
how do they work to get rid of the tumour
the deliberate infection of tumour cells with oncolytic viruses
eg herpes or poliovaccine)
o They can also be engineered to deliver other therapeutic moieties to the tumour such as cytokines
o Often they are engineered to also be less infectious to healthy cells
these viruses alone can induce death of cancer cells AND release of tumour antigens, sparking immune reponses to tumours which may have otherwise been ‘cold’
what is oncolytic virus therapy?
how do they work to get rid of the tumour
the deliberate infection of tumour cells with oncolytic viruses
eg herpes or poliovaccine)
o They can also be engineered to deliver other therapeutic moieties to the tumour such as cytokines
o Often they are engineered to also be less infectious to healthy cells
these viruses alone can induce death of cancer cells AND release of tumour antigens, sparking immune reponses to tumours which may have otherwise been ‘cold’
what is T cell exhaustion?
after continued antigen stimulation CD8+ T cells become exhausted. they upregulate PD1 and Tim3, no longer proliferate or kill infected cells or produce cytokines
thought to limit immunopathology from having chronically activated T cells
occurs with chronic viral infections but also in tumours
what is the major negative regulator of T cells?
o CTLA4 major negative regulator. Initially intracellular – moves to cell surface after TCR signalling (outcompetes the CD28 costimulator)
what are the suppressive co-signalling receptors on T cells
LAG3
TIM3
PD-1
CTLA-4
give two examples of CTLA-4 inhibitor drugs
- Ipilimumab
- Tremelimumab
give two examples of PD-1 inhibitor drugs?
- Nivolumab
- Pembrolizumab
give two examples of PD-L1 inhibitor drugs
- Atezolizumab
- Durvalumab
how successful is checkpoint inhibition?
o 20% of all patients have durable positive results following checkpoint inhibition
very disease and patient specific
o For example, just four doses of anti-CTLA4 have led to 10-year regression in some melanoma patients. Anti-PD1 therapies have a 40% response rate in NSCLC (non small cell lung cancer)
why are immune related adverse effects localised to the intestine?
because millions of T cells resde in the intestinal wall
development of side effects positively correlates with ____________ the tumour
Development of side effects positively correlates with regression of the tumour
what are four ways autoimmunity can develop as a result of T cell treatments?
response dependent toxicity & response independent toxicity
- shared antigens between the tumour and organ site
- pre-existing organ specific inflammation (caused by viral bacterial autoimmune etiologies) is unmasked by treatment
- cytokines and activated T cells generated in an anti-tumour repsonse also result in organ specific inflammation
- CTLA-4 expression on the pituitary gland facilitates T-cell homing when patients are exposed to anti-CTLA-4 antibodies
what are CAR t cells?
made by collecting T cells from the patient and re-engineering them in the laboratory to produce proteins on their surface called chimeric antigen receptors, or CARs.
third generation design - single chain viariant fragment (scFV) (extracellular), a transmembrane domain, & an intracellular CD3 (cosignalling molecule from t lymphocyte)
The CARs recognize and bind to specific proteins, or antigens, on the surface of cancer cells.
what ways/combos can CAR T cells be given for better success?
- Regional injection of cells can be better OR
- Modify the TIL or the CAR-T cells to express chemokine receptors OR / AND
- Infuse alongside activating cytokines
what cytokines have been targetted in anticancer trials for melanoma?
IL-2
IL-15
IL-21
IL-12
GM-CSF
Type 1 IFN
what cytokines have been approved by the FDA to treat hairy cell
type 1 IFN
infusion of what cytokine has been approved by the FDA for melanoma and renal cell
IL-2
give an example of a co-therapy
adoptive transfer of ex vivo-activated T cells WITH anti-PD1 therapy AND recombinant IL-2
what is immunoediting
Immunoediting refers to the concept that the immune system can inadvertently promote this evolution and escape, by killing the cells less able to survive and not clearing the very malignant ones – which then mutate to avoid the immune attack.
how do memory cells form from a vaccine?
6
- dendritic cells collecting some of the injected antigens and taking them to lymph nodes.
- Adjuvants given with the vaccine activate the DC and make them more able to co-stimulate T cells & able to move to the right area.
- In the lymph nodes, the DC present the antigen on their MHC II molecules (to CD4+ T cells) and through cross-presentation to CD8+ T cells on their MHC I molecules.
- The T cells which recognise these peptides as their cognate antigen proliferate and become activated, and move to kill the vaccine peptides.
- The response then resolves and T cells mostly die, with some differentiating into memory cells.
- These memory T cells can live in the tissues or in the blood, and are highly motile as they express lots of chemokine and adhesion protein receptors.
describe the process by which HPV vaccination protects against cervical cancer
8
- The patient is infected with HPV which invades cells of her cervix and begins to malignantly transform them into cervical cancer.
- The cervical cells digest intracellular proteins continually and present these on MHC I molecules on the cell surface. This will include self proteins and also, in the infected cells, HPV proteins.
- Therefore some of the peptides presented in MHC I will be HPV-derived. In addition, some cervical cells will die and the antigens will be collected by dendritic cells, which will take them to the lymph nodes and present both self and HPV antigens to naive T cells.
- Circulating memory T cells move throughout tissues and lymph continually scanning for their own ‘cognate’ antigen.
- Any T cells which recognise the presented HPV peptides will bind to the MHC, as will the CD8 co-receptor, and signalling through the T cell receptor will begin.
- Memory cells react strongly and rapidly to antigen recognition. They proliferate at the site of infection, and can release granzyme, perforin and cytokines in high concentrations.
- This induces apoptosis in the infected cervical cells and the pre-cancerous lesion is cleared.
- Eventually, most of the memory cells die off although some remain to deal with the same challenge again.
